Box Filter

The xFboxfilterfunction performs box filtering on the input image. Box filter acts as a low-pass filter and performs blurring over the image. The xFboxfilterfunction or the box blur is a spatial domain linear filter in which each pixel in the resulting image has a value equal to the average value of the neighboring pixels in the image.

API Syntax

template void xFboxfilter(xF::Mat & _src_mat,xF::Mat & _dst_mat)

Parameter Descriptions

The following table describes the template and the function parameters.:

Table 1.xFboxfilter Function Parameter Descriptions
Parameter Description
FILTER_SIZE

Filter size. Filter size of 3(XF_FILTER_3X3), 5(XF_FILTER_5X5) and 7(XF_FILTER_7X7) are supported

BORDER_TYPE Border Type supported is XF_BORDER_CONSTANT
SRC_T Input and output pixel type. 8-bit, unsigned, 16-bit unsigned and 16-bit signed, 1 channel is supported (XF_8UC1)
ROWS Maximum height of input and output image (must be a multiple of 8)
COLS Maximum width of input and output image (must be a multiple of 8)
NPC Number of pixels to be processed per cycle; possible options are XF_NPPC1 and XF_NPPC8 for 1 pixel and 8 pixel operations respectively.
_src_mat Input image
_dst_mat Output image

Resource Utilization

The following table summarizes the resource utilization of the kernel in different configurations, generated usingVivado HLS 2017.1tool for theXilinx Xczu9eg-ffvb1156-1-i-es1FPGA, to process a grayscale HD (1080x1920) image.

Table 2.xFboxfilter Function Resource Utilization Summary
Operating Mode Filter Size

Operating Frequency

(MHz)

Utilization Estimate
BRAM_18K DSP_48Es FF LUT CLB
1 pixel 3x3 300 3 1 545 519 104
5x5 300 5 1 876 870 189
7x7 300 7 1 1539 1506 300
8 pixel 3x3 150 6 8 1002 1368 264
5x5 150 10 8 1576 3183 611
7x7 150 14 8 2414 5018 942

Performance Estimate

The following table summarizes the performance of the kernel in different configurations, as generated usingVivado HLS 2017.1tool for theXilinx Xczu9eg-ffvb1156-1-i-es1, to process a grayscale HD (1080x1920) image:

Table 3.xFboxfilter Function Performance Estimate Summary
Operating Mode

Operating Frequency

(MHz)

Filter Size Latency Estimate
Max (ms)
1 pixel 300 3x3 7.2
300 5x5 7.21
300 7x7 7.22
8 pixel 150 3x3 1.7
150 5x5 1.7
150 7x7 1.7